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6.1: Introduction to the Skeleton System
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The skeletal system forms the rigid internal framework of the body. It consists of the bones, cartilages, and ligaments. Bones support the weight of the body, allow for body movements, and protect internal organs. Each bone of the body serves a particular function, and therefore bones vary in size, shape, and strength based on these functions.
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6.2: Divisions of the Skeletal System
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The skeleton is subdivided into two major divisions—the axial and appendicular. The axial skeleton forms a vertical axis and the appendicular skeleton includes all of the bones of the upper and lower limbs plus the bones that anchor each limb to the axial skeleton
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6.3: The Skull
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In the adult, the skull consists of 22 individual bones, 21 of which are immobile and united into a single unit. The skull is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the facial bones and the brain case.
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6.4: The Vertebral Column
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The adult vertebral column consists of 24 vertebrae, plus the sacrum and coccyx. The vertebrae are divided into three regions: cervical vertebrae, thoracic vertebrae, and lumbar vertebrae.
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6.5: The Thoracic Cage
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The thoracic cage (rib cage) forms the thorax (chest) portion of the body. It consists of the 12 pairs of ribs with their costal cartilages and the sternum. The ribs are anchored posteriorly to the 12 thoracic vertebrae (T1–T12). The thoracic cage protects the heart and lungs.
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6.6: Embryonic Development of the Axial Skeleton
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The axial skeleton begins to form during early embryonic development. However, growth, remodeling, and ossification (bone formation) continue for several decades after birth before the adult skeleton is fully formed. Knowledge of the developmental processes that give rise to the skeleton is important for understanding the abnormalities that may arise in skeletal structures.